The invention relates to a chuck for tools, especially screwdriver bits with a polygonal section, having a polygonal cavity for the insertion of the polygonal section, the wall of the polygonal cavity having a window in which is disposed a pressure-piece which can be displaced in the insertion direction and which, in order to secure the inserted polygonal section against being drawn out, is forced against the polygonal section, in a direction transverse to the insertion direction, by an actuating element outside the window, in a clamping position of this element, and which, in a release position of the actuating element, can move aside out of the polygonal cavity in order for the polygonal clamping section to be drawn out.
Such a chuck is already known from DE 29 34 428 C2. In this document, the pressure-piece is configured as a ball and is positioned in a window, which is associated with one of the surfaces of the polygon, such that it can be moved in the insertion direction. The window here is in the form of a slot extending in the insertion direction in the cavity wall. Outside the window, the slot is closed by an actuating element which acts on the ball by means of a sloping flank. The actuating element, which is in the form of a sliding sleeve, is biased by spring action in the actuating direction, which extends in the insertion direction. If the polygonal section of a bit is inserted into this chuck, then an annular slope which is arranged at the rear end side of the bit displaces the ball in the insertion direction within the window, in which case the ball, running along the slope of the actuating sleeve, moves out of the polygonal cavity in order to increase the size of the free cross-section. The ball, finally, runs over the end edge of the bit and rests on the surface of the polygon of the polygonal section. If the bit is subjected to a pulling action counter to the insertion direction, then the ball rolls, on the one hand, on the slope of the actuating sleeve and, on the other hand, on the flank of the polygonal section. Since the two surfaces are located in a wedge relationship to one another, this results in clamping.
The disadvantage is that this clamping mechanism does not function when the bit is oriented upward and the ball, in the rear section of the window, lies freely between the flank of the polygonal section and the slope of the actuating sleeve.
The prior art also discloses latching-ball mechanisms in the case of which the ball is located in a window-like cutout which is made in the actuating sleeve and the extent of which in the insertion direction corresponds substantially to the ball diameter, so that the ball can be displaced substantially only transversely to the insertion direction of the bit. The ball is then forced into its blocking position exclusively by the sloping flank of the actuating sleeve. In the case of this chuck, the ball enters into a corner cutout of a bit. Accordingly, it is associated with the edge of the polygon rather than with the surface of the polygon. In the case of this chuck, the actuating sleeve has to be displaced into the release position in order for the bit to be inserted.